LIBRARY 

OF   THK 

UNIVERSITY  OF  CALIFORNIA. 

GIFT    OF 


Class 


UNIVERSITY    OF    CALIFORNIA    PUBLICATIONS 

IN 

ZOOLOGY 

Vol.  4,  No.  3,  pp.  187-226,  Pis.  4-8  March  31,  1908 


CONTRIBUTIONS  FROM  THE  LABORATORY 

OF   THE 

MARINE  BIOLOGICAL  ASSOCIATION  OF  SAN  DIEGO 


XIX 

THE   EARLY  LIFE-HISTORY  OF  DOL1CH- 
OGLOSSUS  PUSILLUS  RITTER 


B.  M.  DAVIS 


UNI 


BERKELEY 

THE   UNIVERSITY  PRESS 


UNIVERSITY    OF    CALIFORNIA    PUBLICATIONS 

Note.— The  University  of  California  Publications  are  offered  in  exchange  for  the 
publications  of  learned  societies  and  institutions,  universities  and  libraries.  Complete 
lists  of  all  the  publications  of  the  University  will  be  sent  upon  request.  For  sample 
copies,  lists  of  publications  or  other  information,  address  the  Manager  of  the  University 
Press,  Berkeley,  California,  U.  S.  A.  All  matter  sent  in  exchange  should  be  addressed 
to  The  Exchange  Department,  University  Library,  Berkeley,  California,  U.  S.  A. 


ZOOLOGY.— W.  E.  Ritter,  Editor.  Price  per  volume  $3.50.  Volumes  I  (pp. 
317),  II  (pp.  382)  and  III  (pp.  383)  completed.  Volume  IV 
in  progress.  Commencing  with  Volume  II,  this  series  contains 
Contributions  from  the  Laboratory  of  the  Marine  Biological 
Association  of  San  Diego. 

Cited  as  Univ,  Cal.  Publ.  Zool. 

No.  1.  The  Ascidians  Collected  by  the  United  States  Fisheries  Bureau 
Steamer  Albatross  on  the  Coast  of  California  During  the  Summer 
of.  1904,  by  Wm.  E.  Ritter.  Pp.  1-52,  plates  1-3.  .  Price,  .50 

No.    2.     Behavior   of  the   Starfish  Asterias   forreri   De  Loriol,    by  H.  S. 

Jennings.     Pp.  53-185,  19  text-figures.         .        .        .      Price,    1.00 

No.    3.    The  Early  Life-history  of  Dolichoglossus  pusillus  Ritter,  by  B.  M. 

Davis.     Pp.  187-226,  Pis.  4-8 Price,       .50 

No.    4.    Notes  on  Two  Amphipods  of  the  Genus  Corophium  from  the  Pacific 

Coast,  by  J.  Chester  Bradley.    Pp.  227-252,  Pis.  9-13.    Price,      .30 


GRAECO-ROMAN   ARCHAEOLOGY.    (Large  Octavo). 

(Published  by  the  Oxford  University  Press.) 

Vol.  1.  The  Tebtunis  Papyri,  Part  1.  1902.  Edited  by  Bernard  P.  Grenfell, 
Arthurs.  Hunt,  and  J.  Gilbart  Smyly.  xix  +  674  pages,  with 
9  plates Price,  $16.00 

Vol.  2.  The  Tebtunis  Papyri,  Part  2.  1907.  Edited  by  Bernard  P.  Grenfell, 
Arthur  S.  Hunt,  and  Edgar  J.  Goodspeed.  xv  -f  485  pages,  with 
2  collotype  plates  and  a  map. 16.00 

Vol.  3..  The  Tebtunis  Papyri,  Part  3  (in  preparation). 

EGYPTIAN  ARCHAEOLOGY.    (Quarto). 

Vol.  1.    The  Hearst  Medical  Papyrus.     Edited  by  G.  A.  Reisner. 

Hieratic  text  in  17  facsimile  plates  in  collotype,  with  introduction  and 
vocabulary,  pages  48, 1905.  (J.  C.  Hinrichs,  Leipzig,  25  Marks) 
Price,  $8.00 

AMERICAN  ARCHAEOLOGY  AND  ETHNOLOGY.  (Octavo). 

Vol.1.     1903-1904.     378  pp.,  with  30  plates Price,  $4.25 

Vol.2.     1904-1907.    392  pp.,  with  21  plates  and  map.      .        .        Price,    3.50 
Vol.  3.    The  Morphology  of  the  Hupa  Language,  by  Pliny  Earle  Goddard. 

Pages  344,  June,  1905 Price,    3.50 

Vol.4.     1906-1907.    356  pp.,  with  10  plates Price,    3.50 

Vol.  5.  No.  1.  The  Phonology  of  the  Hupa  Language:  Part  I,  The  Indi- 
vidual Sounds,  by  Pliny  Earle  Goddard.  Pages  20,  Plates  8, 

March,  1907. Price,       .35 

No.  2.  Navaho  Myths,  Prayers  and  Songs  with  Texts  and  Trans- 
lations, by  Washington  Matthews,  edited  by  Pliny  Earle  Goddard. 
Pages  43,  September,  1907.  Price,  .75 

Vol.6.     No.  1.    The  Ethno-Geography  of  the  Pomo  and  Neighboring  Indians, 

by  S.  A.  Barrett.     Pages  332,  Maps  2,  February,  1908.     Price,    3.25 
No.  2.    The  Geography  and   Dialects  of  the  Miwok  Indians,  by")     In 
S.  A.  Barrett.     Pages  36,  Map  1,  February,  1908.  one 

No.  3.  On  the  Evidences  of  the  Occupation  of  Certain  Regions  }•  cover, 
by  the  Miwok  Indians,  by  A.  L.  Kroeber.  Pages  12,  I  Price, 
February,  1908.  J  .50 


UNIVERSITY   OF  CALIFORNIA    PUBLICATIONS    IN    ZOOLOGY 

Volume  4.     No.  3 

The  Early  Life-History  of  Dolichoglossus  Pusillus  Ritter,  by  B.  M. 
Davis. 

ERRATA  :  On  page  214,  last  line,  for  I),  kowalevskii,  read  B.  Icowalevskii. 
On  page  218,  explanation  of  Plate  4,  last  line,  for  X  1,  read 

X4. 


UNIVERSITY  OF  CALIFORNIA   PUBLICATIONS 

IN 

ZOOLOGY 

Vol.  4,  No.  3,  pp.  187-226,  Pis.  4-8  March  31,  1908 


CONTRIBUTIONS  FROM  THE  LABORATORY 

OF   THE 

MARINE  BIOLOGICAL  ASSOCIATION  OF  SAN  DIEGO. 

XIX 

THE    EARLY   LIFE-HISTORY   OF    DOLICH- 
OGLOSSUS   PUSILLUS   RITTER. 

BY 

B.  M.  DAVIS. 


CONTENTS. 

PAGE 

Introduction    ....................................................  .  ...................................................  188 

Periods  of  Development  ....................................................................................  190 

Early  Habits  and  Activities  of  D.  pusillus  ....................................................  192 

Period  I  ..........................................................................................................  192 

Period  II  ...........................................................  :  ............................................  192 

Period  III  ......................................................................................................  194 

Periods  of  Development  Correlated  with  Habits  and  Distribution  of 
Adults  ........................................................................................................  195 

Early  Growth  Stages  ........................................................................................  200 

External  Features.      Period  I  ..............................................................  .......  200 

Egg     ..........................................................................................................  200 

First  to  Sixth  Cleavages  ......................................................................  201 

Comparison    of   D.   pusillus   with   Amphioxus    and   with   Ascidia 
(dona  intestinalis)  in  their  Early  Cleavage  ..............................  203 

Blastula  ....................................................................................................  204 

Gastrula     ..............................................................................................  204 

Larva  within  the  Egg-capsule  .............................  '.  ..........  ......................  205 

Period  II  ....................................................................................................  205 

Period  III  ................................................................................................  205 

Internal  Features.      Period  I  ...............  ;  ....................................................  205 

Blastula    ....................................................................................................  205 

Gastrula     ........................................................................  :  .........................  206 

Mesoderm  and  Body  Cavities  ...........................  ...................................  207 

Gland  Cells  ..............................................................................................  212 

Occurrence  of  Half  Embryos  and  Double  Embryos  ....................................  213 

Comparison  of  D.  pusillus  and  Amphioxus  with  reference  to  Origin  of 
Body  Cavities  ................................................................................................  213 

Bibliography   ............................................................................................  -  ...........  216 


188         University  of  California  Publications  in  Zoology.    [VOL.  4 


INTRODUCTION. 

In  November,  1902,  I  secured  a  few  eggs  and  free  larvae  of 
D.  pusillus  Hitter,  a  short  account  of  which  is  given  in  a  recent 
paper  (Ritter-Davis  '04).  In  this  account  it  is  stated  that  owing 
to  destruction  of  collecting  grounds  at  San  Pedro,  California,  it 
would  be  impossible  to  secure  a  complete  series  of  stages  necessary 
for  detailed  study,  but  that  it  was  hoped  to  obtain  sufficient  ma- 
terial at  San  Diego,  California.  On  January  18,  1905,  I  had  the 
good  fortune  to  find  a  small  area  of  mud  flats  on  the  west  side  of 
Whaler's  Bight,  San  Diego  Bay,  containing  D.  pusillus  at  the 
height  of  its  breeding  season.  During  the  month  following  (Jan- 
uary 18  to  February  18)  I  succeeded  in  getting  all  stages  from 
iinsegmented  egg  to  metamorphosis,  and  was  able  to  study  these 
stages  in  the  living  condition. 

The  only  account  we  have  of  direct  development  of  Enterop- 
neusta  is  that  by  Bateson  '84- '85.  This  has  become  one  of  the 
zoological  classics.  However,  Bateson 's  series  of  early  stages  was 
not  complete,  and  he  did  not  give  a  detailed  account  of  the  ani- 
mal's activities  at  different  periods  of  its  development. 

Further  investigation  of  the  subject  is  an  urgent  desideratum. 
In  this  paper  I  give  an  account  of  the  habits  and  activities  of  the 
early  life  of  D.  pusillus,  and  also  the  stages  of  development  up  to 
and  including  that  of  the  formation  of  the  body  cavities. 

At  another  time  I  hope  to  follow  out  the  later  stages  of  de- 
velopment, particularly  of  the  connective  tissue  system  and 
supporting  framework.  I  take  pleasure  in  acknowledging  the 
helpful  suggestions  and  directions  which  I  have  received  in  the 
preparation  of  this  paper  from  Professor  William  E.  Ritter. 

MATERIAL  AND  METHODS. 

The  portion  of  the  mud  flats  on  which  the  animals  live  is 
uncovered  at  mean  low  tide  so  that  collecting  is  possible  for 
several  hours  during  five  or  six  days  of  each  low  tide  period. 
This  fact  is  important,  for  the  work  of  collecting  is  slow  and 
tedious,  rs  a  great  many  burrows  must  be  examined  before  one  is 
fourd  contair.ing  eggs. 


1908]  Davis. — Life-history  of  Dolichoglossus.  189 

D.  pusillus  has  its  burrow  near  the  surface,  but  there  are  no 
external  indications  of  its  presence  except  occasionally  when  the 
animal  extends  its  proboscis  from  the  burrow  (Ritter  '02).  A 
certain  amount  of  prospecting  is  therefore  necessary  be~fore  the 
animals  are  found  in  large  numbers. 

When  such  a  place  is  found,  a  spadeful  of  mud  is  dug  up 
and  the  burrow  of  each  animal  carefully  examined  for  eggs.  By 
breaking  one  side  of  the  burrow  and  gently  lifting  the  animal  out 
or  pushing  it  aside,  the  eggs,  if  present,  may  be  seen  clinging  to 
the  unbroken  side.  They  are  usually  closely  packed  and  some- 
times extend  over  an  area  of  several  square  millimeters.  The 
position  of  the  eggs  in  a  burrow  is  shown  in  plate  4.  Here  the 
animal  has  been  lifted  up  and  to  one  side,  leaving  the  eggs  ex- 
posed. The  eggs  are  somewhat  flattened,  whereas  in  water  they 
are  perfectly  round.  They  also  appear  to  be  of  a  darker  tint  of 
yellow  ochre  than  when  seen  in  water.  This  is  due  to  the  dark 
background  of  the  mud. 

From  the  burrow  the  eggs  are  removed  by  means  of  a  fine 
pipette  to  a  shallow  dish  filled  with  clear  water.  By  holding  the 
dish  against  a  white  background,  the  eggs  may  be  easily  sepa- 
rated from  the  particles  of  sand,  and  then  transferred  to  small 
vials  of  sea-water  for  transportation.  As  eggs  or  larvae  of  a 
single  burrow  are  usually  in  nearly  the  same  stage  of  develop- 
ment, when  a  large  number  in  one  burrow  is  found,  they  are  kept 
in  a  separate  vial.  On  reaching  the  laboratory  the  material  is 
transferred  from  vials  to  small  dishes  filled  with  fresh  sea-water. 
An  occasional  change  of  water  is  all  that  is  necessary  to  keep  the 
animals  alive. 

Zenker's  fluid,  corrosive-acetic  mixture,  Lo  Bianco 's  chrom- 
osmic  mixture,  and  osmic  acid  were  used  as  killing  and  fixing 
agents.  After  fixation  and  washing  the  specimens  were  preserved 
in  eighty  per  cent,  alcohol.  Eggs -or  larvae  from  single  burrows 
were  kept  in  separate  dishes.  Some  were  killed  and  preserved 
from  time  to  time,  the  intervals  depending  upon  stage  of  develop- 
ment. Fifteen  such  series  were  made. 

Various  stains  were  used,  including  Mallory's  connective 
tissue  stain,  Meyer's  acid  haemalum,  Benda's  iron  haematoxylin, 
Heidenhain's  iron  haematoxylin,  Delafield's  haematoxylin,  and 


190         University  of  California  Publications  in  Zoology.    [VOL-  4 

borax  carmine.  Congo  red,  erythrosin,  eosin,  and  orange-G  were 
used  as  counter  stains.  Of  these  Meyer's  haemalum  counter- 
stained  with  congo  red  for  the  early  stages,  and  Mallory's  con- 
nective tissue  stain  for  advanced  stages  that  were  fixed  in  Zenker's 
fluid  proved  to  be  the  most  satisfactory. 

Living  material  was  examined  with  a  Zeiss-Greenough  stere- 
oscopic microscope.  The  depth  of  field  and  appearance  of  three 
dimensions  afforded  by  this  instrument  added  greatly  to  the 
accuracy  and  facility  of  observations,  particularly  in  the  detailed 
study  of  swimming. 


PERIODS  OF  DEVELOPMENT. 

The  following  statement  made  in  a  previous  paper  (Kitter- 
Davis  '04,  p.  173)  in  regard  to  periods  of  larval  life  of  Tornaria, 
applies  to  D.  pusillus:  "In  the  larval  life  of  the  enteropneusta 
three  periods  should  oe  recognized;  namely,  a  period  of  larval 
development;  a  climactic  period;  and  a  metamorphic  period;  -i.e., 
a  period  of  development  again,  but  this  time  development  toward 
the  adult  animal." 

As  I  shall  recognize  these  periods  in  my  account  of  the  early 
life  history  of  D.  pusillus,  it  will  be  necessary  to  modify  some- 
what the  definition  previously  given,  particularly  since  no  account 
was  taken  of  the  earliest  developmental  stages  of  tornaria. 

The  first  period,  or  period  of  larval  development,  includes  the 
time  passed  wholly  within  the  egg-membranes.  It  may  be  noted 
that  my  observations  on  the  time  of  hatching  do  not  reveal  any 
such  irregularity  as  described  by  Bateson  for  B.  kowalcvskii. 
After  describing  that  stage  of  the  larva  where  the  collar  area  is 
definitely  marked  off  by  anterior  and  posterior  grooves,  he  says : 
"The  animal  remains  in  this  condition  for  some  hours  and  is 
generally  hatched  without  the  •  occurrence  of  any  further  alter- 
ation. The  time  of  hatching  is,  however,  quite  irregular.  Larvae 
may  frequently  be  found  swimming  freely  whose  organization  is 
not  much  in  advance  of  Stage  C  (the  stage  before  either  groove 
has  appeared),  and  on  the  other  hand,  I  have  seen  them  in  the 
condition  of  Stage  G  (after  appearance  of  first  gill  opening)  in 
the  eggshell."  (Bateson  '84,  p.  211.) 


1908]  Davis. — Life-history  of  Dolichoglossus.  191 

My  observations  agree  substantially  with  the  first  part  of  this 
statement,  but  not  with  that  part  referring  to  irregularity  of 
hatching.  In  his  second  paper  (Bateson  '85,  p.  2)  Jiejsays: 
"From  further  observation  it  seems  probable  that  this  period 
(Stage  D)  assigned  as  the  time  of  hatching  is  too  early;  for 
embryos  kept  in  aquaria  do  not  break  the  membranous  shell  be- 
fore Stage  G  is  reached.  Probably,  therefore,  the  larvae  found 
swimming  in  Stage  D  had  escaped  owing  to  an  artificial  rupture 
of  the  shell  during  the  process  by  which  they  were  found,1  an 
account  of  which  is  given  in  an  appendix. ' ' 

I  am  inclined  to  think  that  the  presence  of  late  unhatched 
larvae  is  also  abnormal  and  exceptional.  As  will  be  described 
in  detail  later,  the  stages  of  normal  larvae  immediately  preceding 
hatching  is  one  of  great  activity  within  the  egg-shell.  It  might 
be  supposed  that  in  exceptional  cases  larvae  would  not  be  suffi- 
ciently active  to  effect  an  opening.  In  such  cases  there  is  no 
apparent  reason  why  the  larvae  should  not  pass  through  the  later 
stages  of  development  within  the  egg-shell;  no  instance  of  this 
kind,  however,  has  come  within  my  observation. 

The  second  or  climactic  period  includes  the  period  of  active 
swimming. 

The  third  or  metamorphic  period  includes  two  phases:  one 
of  rapid  crawling,  mainly  by  means  of  the  ciliary  band,  and  one 
of  slow  crawling,  by  means  of  proboscis  and  body  cilia. 

These  periods  are  not  absolutely  distinct  in  the  sense  of  being 
delimited  from  one  another.  Period  II  gradually  merges  into 
period  III  by  the  active  swimming  cycles,  as  will  subsequently  be 
described,  becoming  less  frequent.  The  same  is  true  of  the  two 
phases  of  period  III,  for  the  movements  by  means  of  proboscis 
and  small  cilia  are  gradually  substituted  for  those  made  by  the 
ciliary  band.  The  three  periods  above  described  will  hereafter 
be  referred  to  by  their  numbers :  I,  II,  III. 


1  The  essential  steps  of  this  process  are  as  follows:  (a)  Shake  up  mud  in 
vessel,  avoiding  rotary  currents;  (&)  put  in  this,  minced  balanoglossus  and 
allow  to  settle  a  few  minutes;  (c)  siphon  off  lighter  particles  in  suspension 
until  balanoglossus  fragments  are  reached;  (d)  draw  this  portion  off  and  in 
it  will  be  found  the  embryos. 


192         University  of  California  Publications  in  Zoology.    tv°L- 4 

EARLY  HABITS  AND  ACTIVITIES  OF  D.  pUSlllllS. 

Period  I. 

As  soon  as  the  ciliary  band  is  fully  formed,  the  larva  begins 
active  swimming  within  the  egg-capsule.  Bateson  '84  (p.  211) 
says:  "The  larva  swims  about  very  rapidly,  rubbing  the  mem- 
branous shell  with  its  anterior  end  until  it  gives  way,  and  the 
animal  escapes."  The  larva  of  D.  pusillus  does  not  escape  as 
easily  as  one  might  suppose  from  the  above  statement.  As  soon 
as  an  opening  is  made,  the  anterior  end  is  pushed  through.  The 
proboscis  becomes  flattened  and  the  body  within  the  capsule  con- 
stricted. '  The  large  cilia  cease  to  move,  but  the  small  ones  are  in 
active  motion,  producing  a  slow  rotation.  The  crucial  point  in 
the  process  of  hatching  is  in  the  passage  of  the  ciliary  band. 
After  this  portion  of  the  body  passes  through  the  opening,  the 
larva  is  soon  free.  The  average  time,  for  the  entire  process  after 
the  opening  is  made,  as  observed  in  five  specimens,  was  twenty 
minutes.  Within  a  few  minutes  after  escape  from  the  egg  the 
larva  begins  active  swimming.  PJate  7,  figs.  17,  a,  1},  and  c,  rep- 
resents the  passage  of  the  larva  through  the  egg  case  opening. 

Period  II. 

As  will  be  noted  in  connection  with  the  description  of  period 
III,  period  II  was  not  noticed  at  San  Pedro.  Bateson  '84  (p.  211) 
says:  "On  leaving  the  egg  it  does  not  swim  at  the  surface  as 
pelagic  larvae  do,  but  creeps  about  in  the  mud,  burrowing  with 
its  proboscis,  in  the  walls  of  which  muscle  fibers  soon  appear,  and 
also  propelling  itself  by  means  of  its  ciliated  band.  If  placed  in 
a  beaker  of  water  it  sinks  to  the  bottom  at  once. ' '  This  descrip- 
tion, with  the  exception  of  one  point,  applies  very  well  to  the 
third  period  of  D.  pusillus,  but  not  to  the  stage  immediately  fol- 
lowing escape  from  the  egg,  or  period  II.  The  exception  above 
noted  is  in  reference  to  what  Bateson  says  of  "burrowing  with 
its  proboscis,  in  the  walls  of  which  muscle  fibers  soon  appear." 
It  is  hard  to  understand  how  the. animal  could  burrow  with  its 
proboscis  before  the  muscle  fibers  appear  and  become  active.  As 
a  matter  of  fact  in  D  pusillus  when  the  burrowing  stage  is  reached 
two  sets  of  muscle  fibers  have  appeared  in  the  proboscis. 


1908] 


Davis. — Life-history  of  Doliclwglossus. 


193 


Period  II  in  D.  pusillus  is  a  time  of  active  swimming,  and 
varies  in  length  from  twelve  to  twenty-four  hours  as  shown  in 
observation  of  twelve  individuals.  Intervals  of  rest  occur,  during 
the  period,  and  these  become  longer  as  the  larva  grows  older. 
When  swimming  actively  the  larva  appears  much  like  a  miniature 
tornaria,  both  in  outline  and  relative  length  of  longer  and  shorter 
axes.  However,  the  similarity  goes  further  than  this.  Like  tor- 
naria it  swims  chiefly  from  below  upward.  It  may  occasionally 
take  a  horizontal  course,  but  this  is  always  undulatory  and  never 
in  a  straight  line.  Like  tornaria,  its  swimming  movements  are 
produced  by  the  cilia  of  the  ciliary  band.  Like  tornaria,  also,  it 
does  not  swim  vertically  upward  but  takes  a  spiral  course,  the 
direction  of  the  spiral,  as  in  tornaria,  being  clockwise. 

Unlike  tornaria,  as  far  as  has  been  observed,  it  has  a  regular 
cycle  of  movements  which  is  repeated  at  rather  regular  intervals. 
Beginning  at  the  bottom  it  swims  vertically  upward  always 
describing  a  spiral.  When  near  the  surface  of  the  water  the 
direction  becomes  horizontal  and  the  path  undulatory  instead  of 
spiral;  then  the  animal  ceases  to  swim  and  falls  rapidly  to  the 
bottom.  The  bottom  having  been  reached,  after  a  short  period 
of  rest,  the  cycle- of  movements  is  repeated.  Sometimes  a  new 
cycle  may  begin  before  the  bottom  is  reached. 

The  following  is  a  tabulation  of  a  typical  series  of  swimming 
cycles : 


Time  of  rising 

through  distance 

Time  of  horizontal 

Time  of                                  Time  of  rest  at 

of  25mm. 

swimming. 

falling. 

bottom. 

40  sees. 

15    sees. 

10  sees. 

No  sees. 

35  sees. 

15    sees. 

8  sees. 

60  sees. 

30  sees. 

Half  way  down  and 

.... 

90  sees. 

new  cycle  begun 

20  sees. 

1  sec. 

30  sees. 

105  sees. 

14  sees. 

No  sees. 

25  sees. 

10    sees. 

11  sees. 

2  sees. 

32  sees. 

1    sec. 

New  cycle  half  wray 

30  sees. 

5    sees. 

New  cycle  one-third 

way  down 

8    sees. 

12  sees. 

6  sees. 

40    sees. 

9  sees. 

70  sees. 

35  sees. 

1    sec. 

New  cycle  two-thirds 

25  sees. 

2    sees. 

way  down 

3    sees. 

8  sees. 

1  sec. 

32  sees. 

1    sec. 

9  sees. 

40  sees. 

19 i         University  of  California  Publications  in  Zoology.    [VOL.  4 

After  several  hours  the  intervals  of  rest  at  the  bottom  grow 
longer  and  longer  until  finally  the  animal  ceases  to  rise.  Light 
does  not  seem  to  have  any  influence  in  directing  the  animal's 
movements.  It  swims  freely  both  toward  and  away  from  the 
light.  A  number  of  animals  were  put  in  a  dish  from  which  light 
was  excluded  except  at  a  small  opening  in  the  cover  of  the  dish. 
The  dish  was  left  undisturbed  for  five  minutes.  At  the  end  of 
this  time  the  animals  were  found  scattered  irregularly  through 
the  water.  This  experiment  was  modified  in  various  ways,  and 
for  varying  lengths  of  time,  but  always  with  negative  results. 

It  is  during  period  II  that  the  tuft  of  apical  cilia  reaches  its 
fullest  development,  although  it  appears  in  period  I.  There  is 
reason  to  suppose  that  these  cilia  are  of  use  to  the  animal  at  this 
time.  It  is  impossible  to  ascertain  their  exact  behavior  when  the 
animal  is  moving  rapidly,  but  when  it  moves  slowly  along  the 
bottom  of  a  dish  by  means  of  the  small  cilia  with  which  the  body 
is  covered,  the  tuft  swings  in  a  direction  opposite  that  which  the 
animal  takes  in  turning,  thus  playing  the  part  of  a  tiller  or  rudder 
for  steering  the  creature.  It  is  probable  that  these  large  cilia 
are  used  in  a  similar  way  during  the  animal's  more  active  move- 
ments. But  the  direction  is  not  determined  entirely  by  the  apical 
cilia,  for  only  one  part  of  the  ciliary  band  may  beat  at  a  time ; 
e.g.,  slow  rotation  is  caused  when  the  cilia  of  one  region  on  one 
side  beat  while  the  rest  are  inactive.  Furthermore,  the  rate  as 
well  as  the  direction  of  swimming  is  determined  by  the  number 
of  cilia  that  beat  in  the  ciliary  band.  The  velocity  of  swimming 
may  be  said  to  vary  with  the  number  of  cilia  in  action.  When 
the  velocity  is  increased,  as  it  always  is  when  the  animal  is  rising, 
this  is  probably  always  accomplished  by  use  of  additional  cilia. 
In  one  portion  of  the  swimming  cycle  the  descent  is  vertical. 
The  cilia  of  the  ciliary  band  are,  at  such  times,  entirely  motionless. 

Period  HI. 

The  few  specimens  examined  at  San  Pedro  in  1902  consisted 
of  unhatched  larvae  (period  I),  and  free  larvae  of  period  III. 
From  the  scanty  material  then  at  hand  I  concluded  with  Bateson 
that  the  first  period  after  hatching  was  a  crawling  one,  and  that 
there  was  no  free  swimming  period.  My  observations  were  de- 


UNIVERSITY 

t)F 


1908]  Davis. — Life-history  of  Dolichoglossus.  195 

scribed  in  these  words:  "Animals  do  not  swim  freely,  but  glide 
about  with  proboscis  pointed  forward  over  the  supporting  surface. 
These  movements  are  made  mainly  by  means  of  the  large  cilia 
composing  the  posterior  ciliated  band,  although  their  action  ceases 
occasionally  for  short  periods.  At  such  times  the  animal  con- 
tinues to  move  by  means  of  minute  cilia  with  which  the  body  is 
covered,  but  the  motion  is  very  slow."  Ritter-Davis  '04,  pp. 
201-202.  This  is  correct  for  the  first  phase  of  period  III.  As 
the  larva  grows  older  there  is  less  and  less  use  of  the  ciliary  band 
until  finally  it  is  not  used  at  all;  at  least  there  is  no  more  rapid 
creeping. 

During  the  latter  part  of  the  first  phase  of  period  III,  at  times 
when  the  ciliary  band  is  not  in  use,  considerable  muscular  activity 
may  be  noticed  in  the  proboscis,  this  member  now  contracting  and 
extending  alternately.  These  movements  are  characteristic  of 
the  second  part  of  period  III.  By  them,  and  also  through  the 
action  of  the  small  body-cilia,  the  animal  is  able  to  creep  slowly 
about  over  the  supporting  surface.  Bits  of  sand  and  other  sedi- 
ment readily  adhere  to  the  body  in  the  region  of  the  collar, 
collected  there  by  the  mucus  or  slime  wrhich  is  actively  secreted 
at  this  time.  The  secretion  in  one  instance  was  so  much  that 
two  larvae  that  happened  to  meet  were  bound  together,  and  so 
closely  that  neither  could  escape  by  its  own  efforts.  In  older 
stages  the  accumulation  of  sediment  was  so  great  as  to  necessitate 
its  removal  before  the  animals  could  be  studied. 

It  is  at  this  time  that  the  larva  begins  to  burrow.  When 
placed  in  a  dish  of  mud  it  soon  disappears  beneath  the  surface. 
The  burrowing  movements  of  D.  pusillus  are  very  similar  to  those 
of  the  larva  described  by  Morgan  '94,  p.  17.  He  says:  "It 
was  very  noticeable  that  so  soon  as  the  proboscis  was  thrust  in 
the  sand  a  thick  mucus  was  thrown  out  from  the  surface  of  the 
proboscis  and  collar  region  to  which  the  sand  granules  stick, 
forming  an  irregular  tube  around  the  animal. ' ' 

Periods  of  development  correlated  with  habits  and  distribution 

of  adults. 

The  adult  life  of  D.  pusillus  is  passed  in  burrows  in  the  mud. 
The  animal  does  not,  as  many  sand-dwelling  animals  do,  come  to 


196         University  of  California  Publications  in  Zoology.    [VOL.  4 

the  surface  and  migrate  to  new  areas.  It  is  true  that  occasionally 
the  proboscis  is  protruded  above  ground,  but  with  the  rising  tide 
this  is  again  withdrawn.  Careful  observations  have  failed  to 
discover  any  instance  where  the  animal's  body  is  in  any  way 
exposed  after  the  ground  is  covered  with  water.  (Ritter  '02, 
p.  255.) 

It  is  also  very  probable  that  any  individual  animal  is  restricted 
to  a  comparatively  small  area ;  that  it  does  not  migrate  from  place 
to  place  in  the  mud.  This  is  indicated  by  the  fact  that  burrows 
are  vertical  for  the  most  part,  and  that  the  burrowing  movements 
'are  slow  compared,  for  example,  with  those  of  certain  nemertians 
and  annelids.  Furthermore,  the  adult  animals  are  not  uniformly 
distributed  over  the  area  in  which  they  are  found.  In  some 
places  as  many  as  fifty  individuals  may  be  found  in  an  area  of 
one  square  foot,  while  in  others  but  one  individual  may  be  found 
in  an  area  of  a  square  yard. 

The  distribution  of  D.  pusillus  during  a  period  of  six  years 
at  San  Pedro,  California,  is  described  as  follows :  * '  The  area  of 
greatest  numbers  has  gradually  shifted  toward  the  mouth  of  the 
harbor.  None  were  found  in  1902  in  places  where  they  were 
abundant  in  1897.  In  1900  there  were  two  areas  of  distribution, 
one  at  low  tide-mark,  where  large  individuals  predominated ;  the 
other  considerably  above  low  tide-mark,  where  small  ones  pre- 
dominated." (Ritter-Davis  '04,  p.  200.) 

Here  are  two  points  worthy  of  notice.  The  shifting  must  not 
be  understood  as  migration  in  the  sense  of  individuals  moving 
toward  the  mouth  of  the  harbor,  but  rather  as  plants  migrate. 
For  various  reasons,  among  them  being  deposition  of  sediment, 
change  of  currents,  and  invasion  of  eel-grass,  the  region  populated 
in  1897  became  unfavorable  for  enteropneust  life,  and  the  animals 
died.  The  opposite  end  of  the  mud-flat  strip  which  was  the 
center  of  distribution  in  1902  became  so  by  the  growth  of  new 
individuals.  In  1900  the  increased  number  of  new  individuals 
was  great  enough  to  be  noticeable  but  in  another  direction  of 
distribution.  Here  they  appeared  farther  shoreward. 

Before  discussing  means  of  dispersal  for  D.  pusillus  it  will  be 
worth  while  to  consider  more  in  detail  the  environment  of  the 
adult.  The  animal  is  always  found  in  sheltered  places,  free  from 


1908] 


Davis. — Life-history  of  Dolichoglossus. 


197 


swift  currents  and  disturbing  waves.  It  is  in  such  places  that 
fine,  black  mud,  rich  in  organic  matter,  occurs.  The  animal  is 
never  found  in  even  moderately  clean  sand. 

The  black-mud  areas  are  associated  with  level  surfaces  which 
are  uncovered  at  low  tide,  with  freedom  from  wave  action,  and 


MAP  OF  PORTION  OF  SAX  DIEGO  BAY. 


1.  Entrance  to  San  Diego  Bay. 

2.  Point  Loma. 

3.  North  Island. 

4.  Spanish  Bight. 

5.  Whaler's  Bight. 

6.  Coronado. 

8.  Government  breakwater. 

Heavy  black  shading  in  4  and  5  indicates  area  of  distribution  of  D. 
pusillus. 

Region  indicated  by  fine  dots  uncovered  at  low  tide. 
Region  indicated  by  large  dots  covered  at  high  tide. 


with  marginal  plant  growth,  part  of  which  is  submerged  at  very 
high  tides.  Whaler's  Bight  and  Spanish  Bight  of  San  Diego  Bay 
are  typical  illustrations  of  just  such  conditions.  The  map 
(p.  197)  is  part  of  the  San  Diego  Bay  including  the  above  bights. 
A  reference  to  this  map  will  indicate  to  what  extent  these  con- 
ditions obtain  in  the  area  of  distribution  of  D.  pusillus. 


198         University  of  California  Publications  in  Zoology.    [VOL.  4 

I  have  already  stated  that  such  situations  are  free  from  swift 
currents  and  strong  waves.  The  tidal  currents  in  these  extensive 
flats  are  unnoticeable  on  casual  observation.  With  this  environ- 
ment in  mind  we  are  ready  to  consider  how  the  early  life-stages 
of  the  animal  are  correlated  with  these  conditions.  Period  I  is 
spent  in  the  egg-capsule  in  the  security  of  the  burrow.  Here  all 
the  developmental  changes,  fitting  the  animal  for  the  active  life 
of  period  II,  take  place,  and  the  beginning  is  made  of  the  organs 
of  greatest  functional  importance  for  period  III,  viz.,  muscles  and 
mucus  glands. 

Although  no  accurate  determinations  were  made  of  the  specific 
gravity  of  the  organism,  it  was  obvious  from  watching  individuals 
of  the  three  periods  that  this  is  least  during  -period  II,  as  in 
tornaria.  The  important  characters  of  period  II  which  are  cor- 
related with  the  animal's  movements  are:  diminished  specific 
gravity,  brought  about,  no  doubt,  in  part  as  will  be  indicated, 
by  the  enlargement  of  the  middle  and  posterior  cavities;  the 
climax  of  efficiency  of  ciliary  activity,  in  both  the  ciliary  band 
and  apical  tuft;  and  absence  of  growth,  except  of  muscles  and 
glands,  whereby  the  animal's  energy  may  be  more  completely 
used  in  swimming. 

The  activities  of  the  organism  at  this  period  are  directed, 
first,  to  escape  from  the  burrow  of  the  parent,  and  second,  to  its 
suspension  in  the  water  during  short  intervals  of  time.  I  say 
"in  suspension,"  for  a  little  calculation  shows  that  it  could  not 
proceed  by  swimming  more  than  two  or  three  meters  during  this 
entire  period,  and  when  we  consider  that  the  direction  of  swim- 
ming is  mostly  vertical,  the  actual  horizontal  progress  would  be 
much  less. 

Obviously,  this  part  of  the  animal's  life  is  adapted  to  make 
use  of  the  slow  tidal  currents  for  dispersal.  Judging  from 
the  numerous  laboratory  experiments  already  described,  the 
swimming  cycles  would  prevent  the  animal  from  being  carried 
very  far  into  deep  water,  for  the  time  of  rest  at  the  bottom  is 
often  greater  than  the  time  of  active  swimming.  Besides  we 
must  also  take  into  consideration  the  fact  that  the  tide  moves  in 
a  direction  away  from  the  deep  water  as  well  as  toward  it.  The 
actual  procedure  from  the  burrow  of  the  parent  is  somewhat  as 


1908]  Davis.— Life-history  of  Dolichoglossus.  199 

follows :  First,  a  cycle  of  swimming  keeps  the  animal  suspended 
for  a  short  time,  during  which  it  is  borne  by  the  tidal  current; 
second,  a  period  of  rest  on  the  surface  of  the  mud,  until  the 
beginning  of  the  next  cycle.  This  process  being  repeated  for 
from  twelve  to  twenty-four  hours",  the  animal  would,  during  this 
time,  be  carried  a  considerable  distance  from  the  parental  burrow, 
at  least  far  enough  to  account  for  such  migrations  as  are  described 
for  San  Pedro  Bay.  (Ritter-Davis  '04.) 

During  the  latter  part  of  this  period  the  intervals  of  rest  are 
longer  and  longer,  until  by  the  time  period  III  is  reached  the 
creature  is  safely  located  in  the  region  of  its  future  burrow. 

What  induces  these  swimming  cycles  is  by  no  means  clear. 
Two  possibilities  are  suggested:  one  of  stimulation,  the  other  of 
rhythmical  physiological  states. 

In  the  consideration  of  stimuli  the  factor  of  light  must  be 
excluded,  since  the  organism  has  been  shown  to  be  indifferent  to 
light.  The  only  source  of  stimulation  would  seem  to  be  contact 
with  the  surface  of  the  mud,  for  temperature,  salinity,  oxygen 
content  of  the  water  and  other  conceivable  factors  are  practically 
constant. 

When  Paramoecium  comes  in  contact  with  a  solid  or  other 
source  of  stimulation,  a  new  cycle  of  movements  is  instituted 
(Jennings  '04).  At  first  thought  it  might  seem  that  the  free- 
swimming  larva  of  D.  pusillus  behaves  in  the  same  way.  If,  as 
it  touches  the  mud  a  new  cycle  were  to  begin  immediately,  the 
behavior  of  the  two  organisms  would  be  essentially  the  same.  But 
the  larva  crawls  for  awhile  on  the  mud,  and  these  crawling 
periods,  even  at  the  height  of  period  II,  vary  in  length.  Again, 
a  new  cycle  is  often  begun  before  the  animal  reaches  the  mud. 
This  precludes  the  possibility  of  contact  as  a  stimulus.  It  would 
seem,  therefore,  impossible  to  assign  any  particular  stimulus  as 
a  cause  for  starting  the  swimming  cycle. 

As  to  these  cycles  being  rhythmical  and  due  to  physiological 
states,  the  chief  objection  is  that  they  are  not  regular  either  in 
point  of  time  or  extent  of  movement.  In  the  behavior  of  Para- 
moecium and  similar  organisms  where  this  explanation  seems 
plausible,  the  animals  are  adults,  and  the  physiological  conditions 
are  fairly  constant.  In  the  animal  under  present  consideration, 


200         University  of  California  Publications  in  Zoology.    [VOL.  4 

the  physiological  conditions  would  not  be  expected  to  be  constant, 
since  they  would  be  interfered  with  by  growth,  which,  though 
reduced,  is  nevertheless  going  on.  But  might  not  the  cycles 
which  would  otherwise  be  rhythmical  due  to  one  set  of  physio- 
logical conditions  be  modified  by  another  set,  e.g.,  that  of  growth, 
so  as  to  bring  about  just  such  irregularity  of  swimming  cycles  as 
is  found?  The  fact  that  these  cycles  become  more  and  more 
irregular  toward  the  end  of  period  II,  when  internal  changes  are 
becoming  more  active  just  previous  to  period  III,  lends  some 
credence  to  this  explanation,  and  makes  it  plausible  but  by  no 
means  certain. 

As  has  already  been  stated,  the  first  phase  of  period  III 
is  characterized  by  rapid  crawling  in  which  the  now  motile 
proboscis  begins  to  take  part.  This  is  an  adaptation  which  is 
important  for  preservation  of  the  animal  at  low  tide,  for  it  is 
enabled  to  burrow  in  the  soft  ooze  and  thus  readily  escape  de- 
struction. 

The  second  phase  is  really  metamorphic.  The  animal's  move- 
ments are  mainly  muscular.  The  mucous  glands  are  sufficiently 
numerous  and  active  to  pour  out  abundant  secretion  for  cement- 
ing the  walls  of  its  burrow  and  lubricating  them  with  slime. 

The  yolk  supplied  by  the  egg  is  now  nearly  used  up  as  in- 
dicated by  the  transparency  of  the  animal  (Bateson  '84),  and 
by  the  absence  of  yolk  granules  as  shown  by  microscopical  exam- 
ination. But  in  the  meantime  a  mouth,  digestive  tract,  and  gills 
have  appeared,  thus  equipping  the  organism  for  self-support. 


EARLY  GROWTPI  STAGES. 

External  Features. — Period  I. 

Egg.  The  method  of  discharging  the  ova,  and  the  general 
characters  of  the  egg  itself  are  adequately  described  by  Ritter- 
Davis  '04.  The  enteropneust  egg  has  two  membranes,  a  fact 
hitherto  unnoticed.  At  first,  these  are  so  closely  adherent  to  each 
other  as  to  be  indistinguishable,  but  later  they  are  separated  by  a 
narrow  space.  The  outer  membrane  may  then  be  removed,  leav- 
ing the  inner  one  intact.  This  is  often  necessary  in  order  to 
study  the  larva  within  the  capsule  when  the  outer  membrane  is 


1908]  Davis.— Life-history  of  Dolichoglossus.  201 

rendered  partially  opaque  by  accumulation  of  sediment.  While 
no  special  observations  were  made  on  the  nature  of  these  mem- 
branes, it  was  noticed  that,  just  before  hatching,  the  outer  one 
became  less  transparent  and  less  resistant.  The  latter-condition 
is  correlated  with  the  hatching  process  which  has  already  been 
described. 

The  particular  feature  of  the  egg  in  this  stage  is  its  opacity. 
Bateson's  statement  that  the  egg  of  D.  kowalevskii  is  "very 
opaque"  is  equally  applicable  to  that  of  D.  pusillus.  The  opacity 
is  due  to  the  yolk  granules  which  are  uniformly  scattered  through- 
out the  cell.  This  distribution  is  so  uniform  that  no  difference 
such  as  described  for  the  ascidian  egg  by  Conklin  and  by  Castle 
may  be  seen  distinguishing  one  part  of  the  cytoplasm  from 
another. 

Cleavage.  Although  I  obtained  many  hundred  eggs  and 
larvae,  I  only  succeeded  in  one  instance  in  finding  the  earliest 
stages.  One  lot  contained  a  few  unsegmented  eggs  and  several 
in  early  cleavage  (four,  eight,  sixteen  cells).  The  material  was 
insufficient  for  a  study  of  the  cell  lineage. 

First  cleavage.  Bateson  '84  (p.  209)  says  of  the  early  cleav- 
age: "The  first  furrow  is  formed  in  a  median  plane,  dividing 
the  ovum  into  two  equal  parts.  It  passes  to  a  considerable  depth. 
With  regard  to  subsequent  segmentation  I  have  no  certain  ob- 
servations; for  though  some  of  the  ova  divided  into  four  and 
eight  nearly  equal  parts,  these  were  obtained  by  artificial  fertil- 
ization, and  the  process  of  division  was  afterwards  continued  in 
an  entirely  abnormal  manner  as  mentioned  above.  Judging, 
however,  from  the  characters  of  the  blastosphere,  and  from  the 
fact  that  yolk  granules  are  uniformly  distributed  through  the 
whole  tissue,  there  can  be  little  doubt  that  the  segmentation  is 
regular  and  complete. ' ' 

I  am  able  to  verify  the  above  observations  in  regard  to  the 
first  cleavage.  (Fig.  3,  pi.  5.) 

Second  cleavage.  (Fig.  4,  pi.  5.)  The  second  cleavage  is  also 
equal,  the  blastomeres  being  arranged  at  first  in  perfect  radial 
symmetry.  In  most  cases  this  symmetry  seems  to  persist,  but  in 
a  few  there  is  a  slight  irregularity.  This  irregularity  was  at  first 
attributed  to  displacement  due  to  manipulation.  While  this  may 


202         University  of  California  Publications  in  Zoology.    [VOL.  4 

be  the  case  it  was  more  likely  normal,  especially  in  view  of  the 
position  of  the  blastomeres  of  some  eggs  of  the  third  cleavage. 
Wilson  '94  has  called  attention  to  the  same  thing  in  Amphioxus : 
"Slight  as  they  are,"  says  this  author,  "they  deserve  attentive 
consideration,  for  they  give,  I  believe,  a  key  to  the  more  consid- 
erable deviations  of  later  stages. ' ' 

Third  cleavage.  (Fig.  5.)  The  third  cleavage  is  unequal  and 
is  of  especial  interest  because  of  its  similarity  to  that  of  Am- 
phioxus. The  blastomeres  of  the  upper  pole  are  smaller  than 
those  of  the  lower.  The  difference  in  size  between  those  of  the 
two  poles  is  somewhat  less  than  that  shown  by  Wilson  for  Am- 
phioxus ;  otherwise  the  two  eggs  are  much  alike  even  to  the 
exception  to  the  usual  bi-lateral  form  of  segmentation,  for  as  in 
Amphioxus  there  occurs  a  deviation  from  the  typical  arrangement 
of  blastomeres  into  the  spiral  form  described  by  Wilson. 

The  slight  irregularity  noted  in  the  second  cleavage  and  the 
spiral  form  in  the  third  cleavage  were  observed  on  preserved 
material.  I  am  therefore  unable  to  say  whether  or  not  the  irreg- 
ular second  cleavage  of  D.  pusillus  gives  rise,  as  Wilson  found  for 
Amphioxus,  to  the  spiral  third  cleavage.  The  early  cleavage 
stages  of  the  two  animals  being  thus  far  so  much  alike,  and  also 
in  other  respects  to  be  described,  suggest  that  they  may  be  found 
to  be  alike  in  this  particular  also. 

Fourth  cleavage.  (Fig.  6.)  The  typical  fourth  cleavage  is 
shown  in  fig.  6.  Here  it  will  be  seen  that  the  cleavage  is  bi-lateral. 
All  eggs  observed  in  this  stage,  except  one,  were  of  this  form. 
This  one  exception  corresponds  to  Wilson's  mixed  form  of 
cleavage. 

Fifth  cleavage.  (Fig.  7.)  In  the  fifth  cleavage  another  point 
of  similarity  between  D.  pusillus  and  Amphioxus  is  to  be  ob- 
served: the  presence  of  a  cleavage  pore.  This  and  the  bi-lateral 
form  of  cleavage  is  shown  in  fig.  7.  A  large  per  cent,  of  eggs  of 
this  stage  and  stages  immediately  following  possessed  cleavage 
pores. 

Sixth  and  subsequent  cleavages.  The  sixth  and  subsequent 
cleavages  do  not  show  clearly  a  bi-lateral  symmetry.  Two  of 
these  stages  are  shown  in  figs.  8,  9,  pi.  5. 

Comparison  of  D.  pusillus  with  Amphioxus.     Although  my 


1908]  Davis. — Life-history  of  Dolichoglossus.  203 

observations  as  above  recorded  were  made  upon  few  individuals 
they  are  sufficient  to  warrant  pointing  out  the  great  similarity 
between  the  early  cleavage  of  this  animal  and  Amphioxus.  A 
reexamination  of  plenty  of  material  and  a  careful  study  of  the 
cell-lineage  of  D.  pusillus  would  no  doubt  show  a  greater  like- 
ness. The  points  of  similarity  are : 

(a)  Bi-lateral  form  of  cleavage,  as  a  rule. 

(b)  Occasional  variation  from  this  into  spiral,  and  perhaps 
into  radial  and  mixed  cleavage. 

(c)  Frequent  occurrence  of  a  cleavage  pore. 

(d)  Gradual  obliteration,  in  later  stages,  of  bi-lateral  sym- 
metry. 

The  points  of  difference  are : 

(a)  Absence  of  radial  cleavage  in  D.  pusillus.  But  since 
there  was  one  instance  of  mixed  cleavage,  it  is  not  unlikely  that 
in  a  large  number  of  individuals  in  early  cleavage  some  of  this 
form  might  be  found. 

(6)  Less  difference  in  the  size  of  the  blastonieres  of  the  two 
poles  of  the  third  cleavage  in  D.  pusillus  than  in  Amphioxus. 
This  point,  however,  is  unessential  since  the  yolk  is  uniformly 
distributed  in  the  eggs  of  both  animals,  and  the  stages  subsequent 
to  the  third  cleavage  are  alike  as  far  as  can  be  shown  with  the 
material  at  hand. 

Comparison  of  D.  pusillus  and  Amphioxus  with  Ascidia  (Ciona 
intestinalis)  in  their  early  cleavage.  Castle  and  Conklin  were 
able  to  recognize  that  the  unsegmented  ovum  of  Ascidia  is  made 
up  of  two  unlike  hemispheres,  one  richer  in  yolk  and  the  other 
richer  in  protoplasm.  Castle  '96  concludes:  "The  form  and 
rate  of  cleavage  are  therefore  manifestly  predetermined  by  the 
internal  constitution  of  the  ovum."  In  the  Enteropneust  egg 
(D.  pusillus)  and  in  the  egg  of  Amphioxus  no  such  distribution 
of  yolk  and  protoplasm  occurs. 

With  reference  to  symmetry  of  cleavage  Castle  '96  (p.  233) 
says:  "Wilson  '94  observed  that  the  cleavage  of  Amphioxus 
showed  all  gradations  between  a  perfectly  radial,  a  bi-lateral,  and 
even  a  spiral  form ;  and  raised  a  query  whether  the  same  might 
not  be  true  for  Ascidians.  In  Ciona  at  least  this  does  not  seem 
to  be  the  case.  I  have  never  observed  an  instance  of  deviation 


204         University  of  California  Publications  in  Zoology.    [VOL.  4 

from  the  regular  mode  of  cleavage  described  in  the  foregoing 
paper."  By  "regular  mode"  he  means  bi-lateral.  He  adds 
further :  "In  having  a  perfectly  definite  and  stereotyped  manner 
of  cleavage,  the  Ascidian  egg  resembles  more  closely  the  egg  of 
Annelids,  Mollusks,  and  the  great  majority  of  invertebrates  than 
it  does  Amphioxus  and  the  vertebrates,  notwithstanding  that  the 
end  product  of  cleavage  shows  unmistakably  the  now  generally 
admitted  closer  affinity  of  the  tunicates  with  the  latter  group  of 
animals." 

One  must  conclude  from  this  and  from  what  has  been  indi- 
cated in  the  comparison  of  D.  pusillus  with  Amphioxus  that,  in 
so  far  as  resemblance  in  cleavage  may  be  relied  upon  for  deter- 
mining affinities,  there  is  a  closer  relation  between  these  two 
animals  than  between  Ascidia  (Ciona)  and  Amphioxus. 

Blast  ula.  The  blastocoele  appears  as  a  segmentation  cavity 
as  early  as  the  fourth  cleavage,  so  that  it  is  difficult  to  set  apart 
the  stages  of  cleavage,  just  described,  from  the  blastula. 

I  shall  regard  the  stage  just  succeeding  that  shown  in  fig.  9, 
as  the  early  blastula  stage,  for  it  corresponds  to  the  earliest  stage 
that  Bateson  found  beyond  the  first  cleavage  and  which  he  calls 
the  blastosphere.  He  describes  it  as  spherical,  with  opaque  walls, 
though  "the  outline  of  cells  composing  them  could  be  faintly 
distinguished  in  a  surface  view. ' ' 

I  did  not  find  among  my  living  stages  of  the  blastula  the 
elliptical  form  described  by  him  for  the  later  stages;  but  in 
preservation  some  became  elliptical.  I  did,  however,  observe  the 
slightly  flattened  condition  which  he  describes  as  just  preceding 
gastrulation. 

Gastrula.  Estimated  from  the  time  eggs  were  taken  from  the 
burrow  when  segmentation  no  doubt  was  beginning,  until  the  first 
evidence  of  gastrulation,  about  twenty  hours  elapsed  (figs.  10 
and  11).  Bateson 's  account  of  external  changes  of  this  period 
agrees  largely  with  my  own  observations. 

The  flattened  condition  of  the  gastrula  remains  but  for  a  short 
time.  Before  the  ring  of  cilia  appears  the  gastrula  is  nearly 
spherical.  In  this  respect  it  differs  from  B.  kowalevskii. 

The  time  between  the  beginning  of  gastrulation  and  the  ap- 
pearance of  cilia  is  about  twelve  hours.  The  blastopore  can  no 


1908]  Davis. — Life-history  of  Dolichoglossus.  205 

longer  be  seen  from  the  surface  but  sections  show  that  it  does  not 
completely  close  until  about  six  hours  later. 

Larva  within  the  egg-capsule.  The  larval  period  may  be  said 
to  begin  with  the  closure  of  the  blastopore  and  elongatiorLof  the 
body.  This  elongation  is  at  right  angles  to  the  plane  of  the  ciliary 
band.  I  was,  unfortunately,  not  able  to  determine  the  relation 
of  the  axis  of  the  embryo  to  the  first  cleavage  plane. 

The  most  important  changes  that  take  place  are:  growth  in 
length,  enlargement  of  the  ciliary  band,  appearance  of  the  pos- 
terior collar  groove  and  later  of  the  anterior  groove ;  and  devel- 
opment of  the  anterior,  or  apical  cilia.  (Figs.  13,  14,  pi.  6.) 
As  these  changes  are  fully  described  by  Bateson  '84  and  are  so 
closely  repeated  in  the  present  species  I  need  not  here  discuss 
them. 

Period  II. 

The  larva  remains  through  this  period,  in  external  appear- 
ance, just  as  when  leaving  the  egg,  except  perhaps  for  a  slight 
elongation  of  the  body.  (Fig.  15,  pi.  6.)  The  significance  of 
this  quiescent  stage  has  already  been  discussed  in  another  con- 
nection. 

Period  III. 

Like  period  I,  this  period  is  marked  by  many  changes :  further 
elongation  of  body,  both  of  proboscis  and  body  proper;  appear- 
ance of  gill  openings;  disappearance  of  apical  cilia,  and,  later, 
reduction  of  the  ciliary  band ;  increase  in  diameter  and  width  of 
collar.  (Fig.  16,  pi.  6.)  I  have  nothing  to  add  to  Bateson 's 
(pp.  211-213)  full  description  of  the  external  appearance  of  the 
stages  of  this  period.  My  own  observations,  except  for  slight 
details,  agree  with  his. 

Internal  Features. — Period  I. 

Blastula.  The  first  internal  change  to  be  noticed  is  in  the 
latter  part  of  this  period.  The  cells  forming  that  portion  of  the 
blastosphere  which  is  to  be  invaginated  (endodermal  portion) 
are  somewhat  irregular,  having  rounded  ends  projecting  un- 
evenly into  the  blastocoele.  (Fig.  18,  pi.  7.)  They  are  relatively 
narrower  than  the  cells  of  the  opposite  portion  of  the  blastosphere 


206 .        University  of  California  Publications  in  Zoology.    [VOL-  4 

(ectodermal  portion),  probably  indicating  more  rapid  cell  divi- 
sion in  this  region. 

Numerous  large  round  cells,  many  of  them  in  mitosis,  are  to 
be  seen  near  or  at  the  surface  of  both  the  ectodermal  and  endo- 
dermal  portions  of  the  blastosphere.  These  cells  are  further 
distinguished  from  the  remaining  cells  by  having  different  stain- 
ing properties  of  the  cytoplasm.  One  of  them  is  shown  in  fig.  18, 
g.  c.  None  were  noticed  earlier. 

Bateson  found  a  greater  difference  between  the  ectodermal 
and  endodermal  portions  of  the  blastosphere  than  I  have  just 
described.  He  did  not,  however,  notice  the  presence  of  the  round 
cells,  above  mentioned,  which  are  very  conspicuous  in  this  and 
later  stages  of  D.  pusiUus. 

Gastrula.  The  gastrula  is  formed  by  the  invagination  of  the 
endodermal  portion  of  the  blastosphere,  and  elongation  in  the 
direction  of  a  line  passing  through  the  center  of  the  blastopore 
and  opposite  pole.  As  elongation  proceeds  the  endoderm  ap- 
proaches the  ectoderm  until  the  two  layers  meet.  At  the  same 
time  the  blastopore  is  closing. 

Fig.  19,  pi.  7,  shows  the  early  stage  of  gastrulation  before 
elongation.  It  will  be  noticed  that  the  endoderm  is  somewhat 
thinner  than  the  ectoderm,  and  that  there  is  less  difference  in  the 
histological  character  of  the  cells  than  in  the  stage  just  preceding 
invagination.  The  rounded  ends  of  the  endodermal  cells  and 
indications  of  their  being  amoeboid,  as  described  by  Bateson  '84 
(p.  213),  I  was  unable  to  find. 

Fig.  20  is  a  longitudinal  section  through  the  blastopore  at  the 
last  stage  of  gastrulation.  Here  the  blastopore  is  about  closed, 
and  the  two  layers  are  adjacent.  The  cells  of  the  region  of  the 
blastopore  are  irregular  and  in  rapid  division  as  indicated  by  the 
numerous  nuclei.  The  ectodermal  part  of  the  blastoporic  rim  is 
already  in  process  of  fusion.  Later  the  endodermal  part  fuses, 
and  thus  the  blastopore  is  completely  closed.  The  ectoderm  and 
endoderm  of  this  region  remain  coalescent  for  a  time  (fig.  21), 
but  finally  separate  (fig.  22,  pi.  7). 

In  this  manner  the  gastrula  passes  into  what  Bateson  (p.  215) 
calls  a  " two-walled  cylinder,"  the  outside  wall  of  which  is  the 
ectoderm,  and  the  inside  the  endoderm.  With  the  exception 


1908]  Davis. — Life-history  of  Dolichoglossus.  207 

already  noted,  my  observations  on  this  stage  agree  with  Bateson  '& 
account.  I  have,  therefore,  omitted  many  details. 

Mesoderm  and  body  cavities.  Bateson  (p.  214)  gays  of  the 
two-layer  stage  just  described:  "The  hypoblast  of  the  middle 
region  is  seen  to  be  more  columnar  in  character  than  that  of  the 
anterior  region,  while  the  other  appearances  are  the  same. ' '  Fig. 
22  shows  this  condition.  It  will  be  noticed  that  the  cells  of  the 
extreme  anterior  are  somewhat  shortened.  The  cells  at  the  trans- 
ition from  the  anterior  to  the  middle  region  tend  to  lose  their 
columnar  character  and  to  become  irregular.  Here,  as  we  shall 
see,  is  the  beginning  of  a  series  of  changes  in  the  endodermal 
cylinder  which  is  to  give  rise  to  the  mesoderm. 

Since  Spengel  '04  associates  the  formation  of  the  mouth  with 
the  origin  of  the  mesoderm  in  tornaria  it  may  be  worth  while  to 
state  that  according  to  Bateson 's  observations  on  B.  Kowalevskii 
and  my  own  on  D.  pusillus  the  mouth  does  not  appear  until  after 
the  mesoderm  is  formed. 

By  the  time  the  two  layers  in  the  blastoporic  region  have 
become  separated,  that  portion  of  the  endoderm  which  has  just 
been  described  as  composed  of  irregular  cells  (fig.  22)  has  pro- 
jected outward  and  backward  somewhat,  thus  partially  separating 
the  archenteron  into  anterior  and  posterior  parts.  The  former 
will  be  referred  to  as  "anterior  body  cavity"  (Bateson  '84,  p. 
216).  This  stage  of  development  is  shown  in  fig.  23,  pi.  8.  It 
will  be  seen  that  the  cells  of  the  walls  of  the  anterior  cavity  are 
becoming  irregular,  especially  on  the  sides,  and  that  some  cells 
are  being  budded  off  into  the  cavity.  Rapid  growth  and  redis- 
position  of  cells  continue  until  the  condition  shown  in  fig.  24  is 
reached.  Here  the  anterior  body  cavity  although  irregular  shows 
the  beginning  of  a  lateral  and  backward  projection.  The  walls 
of  the  anterior  body  cavity  and  those  of  the  archenteron  are 
sharply  differentiated  in  character  of  their  cells.  The  archen- 
teron will  henceforth  be  referred  to  as  enteron. 

The  lateral  backward  projections  of  the  walls  of  the  anterior 
body  cavity  continue  to  grow.  The  next  two  stages  are  shown  in 
fig.  25  and  fig.  26,  pi.  8. 

It  must  be  here  noted  that  the  backward  growth  is  not  only 
lateral,  but,  for  a  short  distance,  dorsal  as  well.  There  is  no 


208         University  of  California  Publications  in  Zoology.    [VoL-  4 

ventral  extension,  so  that  the  mesoderm  forms  a  broken  ring 
around  the  anterior  extremity  of  the  enteron  (fig.  27).  From 
this  point  the  mesodermal  growth  is  confined  to  the  sides.  (See 
quotation  from  Bateson.) 

The  following  description  refers  exclusively  to  the  lateral 
backward  growth  of  the  mesoderm.  In  the  section  represented 
in  fig.  24,  pi.  8,  it  will  be  seen  that  the  walls  of  the  enteron  are 
completely  separated  from  the  anterior  body  cavity  except  at  one 
point.  Complete  separation  is  seen  in  stages  represented  by 
figs.  27  and  28.  The  walls  of  the  anterior  body  cavity  may  now 
be  called  mesoderm.2  The  edges  of  the  anterior  portion  of  the 
enteric  walls  are  approaching,  leaving  a  small  oblong  communi- 
cation (oblong  dorso-ventrally)  between  the  two  cavities. 

The  growth  of  the  mesoderm  backward  is  taking  place  wedge- 
wise  between  the  walls  of  the  enteron  and  the  ectoderm.  The 
cells  of  the  edge  are  irregular,  tending  somewhat  to  flatness  at 
its  narrow  extremity.  In  this  way  the  mesoderm  continues  to 
grow  backward,  the  wedge  of  cells  (as  seen  in  longitudinal  sec- 
tion) becoming  somewhat  longer  and  thinner,  and  reaching  be- 
yond the  collar  region.  This  stage  of  development  is  shown  in 
fig.  25.  At  a  little  later  period  an  important  change  takes  place. 
The  mass  of  cells  extending  backward  between  the  enteric  wall 
and  the  ectoderm  loses  its  wedge-shape  in  longitudinal  section. 
At  a  point  corresponding  to  the  anterior  collar  groove,  the  mass 
of  cells  is  slightly  constricted.  In  the  collar  region  corresponding 
in  longitudinal  extent  to  the  collar,  the  cells  form  two  layers. 
Posterior  to  this  region  the  mesoderm  continues  for  a  short  dis- 
tance as  a  single  layer  of  somewhat  flattened  cells.  (Fig.  26.) 
This  is  the  beginning  of  the  middle  body  cavity. 

The  mesoderm  grows  backward  until  it  almost  reaches  the 
posterior  extremity  of  the  enteron.  In  the  meantime  a  second 
constriction  occurs  at  a  point  corresponding  to  the  posterior 
groove  of  the  collar  (fig.  28,  pi.  8).  Posterior  to  this  constriction 
tin-  mesoderm  forms  two  layers  just  as  described  above  for  the 
collar  region. 

In  this  manner  the  middle  and  posterior  body  cavities  arise 

•  The  term  mesoderm  has  already  been  used  in  reference  to  the  portion  of 
this  region  which  is  reflected  backward. 


UNIVERSITY    j 

OF 


1908]  Davis. — Life-history  of  Dolichoglossus.  209 

from  the  mesoderm.  Their  walls  are  one-cell  deep,  the  cells  be- 
coming flattened.  For  a  while  the  three  body  cavities,  anterior, 
middle,  and  posterior,  are  continuous,  though  marked  ^ff  by  the 
constrictions  already  described.  Fig.  29,  pi.  8,  shows  the  relation 
of  these  cavities  to  one  another  at  this  stage.  Subsequently  the 
constrictions  deepen  until  finally  they  completely  separate  the 
cavities. 

Prior  to  this  period  the  middle  and  posterior  cavities  have 
extended  ventrally  somewhat,  but  more  dorsally.  This  growth 
continues  concomitantly  with  the  later  stages  of  longitudinal 
growth  just  described.  They  extend  dorsally,  meeting  at  the 
mid-dorsal  line,  but  ventrally  they  do  not  quite  meet. 

As  the  above  account  of  the  origin  of  the  middle  and  posterior 
body  cavities  in  D.  pusillus  is  at  absolute  variance  with  Bateson's 
description  of  the  origin  of  these  structures  in  B.  kowalevskii,  and 
with  his  diagram,  familiar  in  text-books,  I  wish  to  review  his 
account  somewhat  fully. 

After  describing  the  stage  corresponding  to  that  in  D.  pusillus 
shown  in  fig.  23,  pi.  8,  he  says:  "The  mesoblast  arises  at  this 
period  of  development.  It  is  formed  directly  by  differentiation  of 
cells  belonging  to  the  archenteron.  These  differentiations  occur 
in  five  regions.  The  first  comprises  a  median  and  primitively- 
unpaired  tract  in  the  anterior  end,  which  forms  the  lining  of  the 
body  cavity  of  the  praeoral  lobe.  Behind  this  anterior  body 
cavity  a  pair  of  mesoblastic  differentiations  occur  in  the  region 
of  the  collar,  constituting  lateral  outgrowths  of  the  archenteric 
walls,  each  containing  a  cavity  which  communicates  directly  with 
the  cavity  of  the  archenteron.  Behind  these,  again,  is  another 
pair  of  regular  archenteric  diverticula,  in  the  region  of  the 
trunk."  He  refers  at  this  point  to  his  well  known  diagram 
illustrating  his  description. 

He  then  describes  in  detail  (pp.  141-142)  the  development  of 
the  anterior  body  cavity.  The  latter  part  of  his  description  (pp. 
218-219)  is  as  follows: 

' '  Now,  since  the  anterior  body  cavity  is  continued  behind  the 
end  of  the  gut  on  all  sides  excepting  the  ventral,  it  is  crescentic 
in  shape,  the  concavity  being  directed  downwards.  This  appear- 
ance exists  only  for  a  short  distance.  Behind  it  the  continuity 


210         University  of  California  Publications  in  Zoology.    [VoL- 4 

across  the  dorsal  surface  ceases,  and  the  mesoblast  exists  as  a  pair 
of  small,  hollow  cavities  at  the  dorso-lateral  sides  of  the  gut,  which 
is  here  much  more  fully  developed,  occupying  most  of  the  space 
enclosed  by  the  epiblast.  Still  farther  backward  the  cavities  in 
these  two  mesoblastic  tracts  close  up,  and  their  walls  are  continued 
for  a  short  distance  as  two  solid  cords  of  cells,  and  then  disappear. 

"The  mesoblast  of  the  anterior  body  cavity  is,  therefore, 
formed  directly  from  the  walls  of  the  hypoblast,  which  occupied 
the  same  situation.  It  is  separated  off  from  it  by  a  process  of 
constriction  in  the  region  of  the  external  groove,  dividing  the 
proboscis  from  the  collar.  While  this  process  of  constriction  is 
being  carried  out,  the  pouch  of  mesoblast  grows  backwards,  sur- 
rounding the  gut  except  on  the  ventral  surface,  but  especially 
forming  the  hollow  horns."  (Italics  mine.) 

The  description  which  I  have  just  quoted  agrees  substantially 
with  my  own  observations  of  the  origin  and  first  stages  of  devel- 
opment of  the  mesoblast  in  its  relation  to  the  anterior  body  cavity. 
The  portions  of  his  description  of  the  lateral  backward  growths 
of  the  mesoblast  which  I  have  italicized  is  almost  an  exact  account 
of  the  stage  which  I  have  shown  in  fig.  26,  and  I  believe  must 
correspond  to  it.  As  I  have  shown,  the  mesoderm  already  grow- 
ing backwards  continues  to  do  so  at  the  sides,  finally  forming  the 
middle  and  posterior  body  cavities.  This  conclusion  is  based  on 
an  examination  of  a  large  number  of  sections  (about  one  hundred 
and  fifty  series  of  sections),  a  typical  series  of  which  I  have 
shown  in  my  figures.  Nowhere  have  .1  seen  any  indication  of  a 
communication  between  any  one  of  the  middle  or  posterior  cavities 
with  the  enteric  canal.  Neither  have  I  seen  any  evidence  of  de- 
lamination  of  the  enteric  wall.  Throughout  all  the  stages,  from 
the  two-walled  cylinder  to  that  of  the  fully  formed  body  cavities, 
the  walls  of  the  enteron  in  the  region  of  the  middle  and  posterior 
body  cavities  show  no  histological  difference  from  other  parts  of 
the  wall.  Whereas  the  cells  bounding  these  cavities  are  very 
different  from  the  cells  making  up  the  wall  of  the  enteron. 

Concerning  the  connection  between  the  middle  body  cavities 
and  the  archenteron  Bateson  '84  (p.  220)  says:  "This  condition 
is  only  visible  in  a  very  few  of  the  larvae,  and  may  possibly  be 


1908]  Davis. — Life-history  of  Dolichoglossus.  211 

due  to  the  action  of  reagents.  Since,  however,  the  middle  meso- 
blastic  tracts  in  Tornaria  are  said  to  be  archenteric  diverticula 
(Spengel,  etc.),  it  seems  more  likely  that  the  rarity  of  their 
occurrence  is  due  to  the  shortness  of  the  time  for  which  they  are 
present. ' ' 

Of  the  connection  between  the  posterior  body  cavities  and  the 
archenteron  he  is  more  certain.  He  says  (p.  221)  :  "These 
mesoblastic  pouches  open  by  large  foramina  into  the  lumen  of 
the  gut. ' '  No  such  large  foramina  exist  in  any  stage  that  I  have 
studied  in  D.  pusillus.  Although  Spengel  '77,  several  years  be- 
fore Bateson 's  paper,  held  that  the  middle  mesoblastic  tracts  in 
Tornaria  are  "archenteric  diverticula,"  he  later  modified  this 
view,  for  he  says  (Spengel  '94,  p.  431)  :  "dass  die  beiden  Co- 
lome  jeder  Seite  aus  einer  gemeinschaftlichen  Anlage  hervorge- 
hen,  die  spater  in  zwei  Theile  zerf allt. ' ' 

I  cannot  but  think  that  Bateson  failed  to  notice  the  connecting 
links  between  the  mesoderm  of  the  anterior  body  cavities  and 
that  of  the  other  cavities,  for  his  observations  of  the  early  back- 
ward growth  of  the  mesoderm,  as  well  as  of  the  cavities  after 
being  formed,  agree  with  mine.  Indeed,  his  fig.  36  shows  a  com- 
munication, or  at  least  a  close  connection,  between  the  middle 
and  posterior  body  cavities  just  as  I  have  shown  in  my  fig.  28. 
The  only  essential  difference  between  his  figure  and  mine  will  be 
seen  to  be  in  the  definite  line  which  he  has  drawn  separating  the 
anterior  from  the  middle  body  cavity.  Such  a  separation  does 
not  occur  in  my  sections  of  the  same  stage. 

Furthermore  the  archenteric  walls  in  the  region  of  the  middle 
and  posterior  cavities  at  no  time  show  any  evidences  of  out- 
pocketing.  If  these  cavities  were  outgrowths  of  the  archenteric 
wall  one  would  expect  to  find  evidences  of  this  growth  in  the 
disposition  of  the  cells  of  these  regions.  In  the  early  stages  of 
the  anterior  cavity  the  cells  of  the  portion  of  the  archenteron 
giving  rise  to  it  are  irregular  both  as  to  shape  and  arrangement. 
The  same  condition  is  observed  at  the  blastopore  at  the  time  of 
its  closure.  But  no  such  irregularity  is  ever  noticed  in  the  arch- 
enteric  walls,  where  according  to  Bateson  the  middle  and  pos- 
terior outgrowths  occur. 

Morgan  '94  does  not  accept  Bateson 's  account  of  the  origin 


212         University  of  California  Publications  in  Zoology.    [VOL.  4 

of  the  second  and  third  body  cavities  as  will  be  seen  from  the 
following  (p.  70)  :  "The  collar  cavities  are  said  to  arise  by  a 
pair  of  lateral  evaginations  from  the  archenteron.  For  the 
present  I  accept  this  account  of  the  origin  of  the  second  pair  only 
tentatively.  The  evidence  furnished  by  Bateson  does  not  seem 
to  me  conclusive  for  accepting  his  statement.  I  think  the  phe- 
nomena could  be  explained  by  a  process  of  delamination  or 
migration,  and  a  subsequent  opening  (or  perhaps  the  small  open- 
ings are  artifacts) . ' ' 

If  one  may  judge  from  his  descriptions  and  figures,  Bateson 
relied  in  his  studies  mainly  upon  transverse  sections,  whereas 
the  relation  of  the  cavities  to  one  another  may  be  more  certainly 
followed  on  horizontal  longitudinal  sections.  But  these  sugges- 
tions hardly  suffice  to  harmonize  our  observations.  The  other 
alternative  is  that  B.  kowalevskii  and  D.  pusillus,  though  so  much 
alike  in  most  respects,  differ  widely  in  the  origin  and  development 
of  their  middle  and  posterior  body  cavities.  But  this  is  hardly 
probable. 

Gland  cells.  One  characteristic  of  the  Enteropneusta  is  the 
presence  of  numerous  unicellular  glands  in  the  epidermis.  Allu- 
sion has  already  been  made  to  the  very  active  secretion  of  these 
glands  which  occurs  in  period  III.  I  have  also  called  attention 
to  certain  large  round  cells  which  make  their  appearance  on  the 
periphery  of  the  blastula. 

Those  that  happen  to  be  on  the  endodermal  portion  of  the 
blastula  are  invaginated  during  gastrulation.  They  persist  a 
while  in  the  endoderm,  but  I  was  unable  to  determine  their  sub- 
sequent fate. 

The  cells  which  are  in  the  ectoderm  increase  in  number 
throughout  the  subsequent  stages.  During  the  latter  part  of 
period  I  some  of  these  are  made  deep  blue  by  Mallory  stain,  indi- 
cating the  mucous  character  of  their  contents. 

In  period  II  they  become  numerous  in  the  collar  region,  and 
at  the  two  extremities.  Some  are  empty;  others  are  full  of 
secretion. 

In  the  early  part  of  period"  III  the  number  in  the  collar  region 
is  so  great  as  to  form  an  almost  continuous  layer.  Here,  in 
Mallory-stained  sections,  the  collar  presents  a  deep  blue  border, 


1908]  Davis. — Life-history  of  Doliclwglossus.  213 

with  here  and  there  light  spots  indicating  the  position  of  cells 
from  which  secretion  has  been  discharged. 

OCCURRENCE  OF  HALF  EMBRYOS  AND  DOUBLE  EMBRYOS. 

The  blastomeres  of  the  early  cleavages  are  loosely  held  to- 
gether. This  fact  may  account  for  the  appearance  of  various 
small  embryos.  No  careful  study  was  made  of  them;  indeed  a 
great  many  were  destroyed  or  not  preserved.  From  the  few 
notes  I  made  the  following  may  be  of  interest,  particularly  in 
view  of  the  recent  studies  in  the  development  of  egg  fragments. 

The  occurrence  of  what  may  be  called  half  embryos  was  noted 
in  several  stages.  The  earliest  was  where  two  blastomeres  of  the 
four-celled  stage  had  been  destroyed.  The  next  stage  observed 
consisted  of  eight  blastomeres.  This  stage  corresponds  to  the 
third  cleavage  except  in  the  smaller  size  of  the  blastomeres. 
Another  stage  was  an  early  blastula  about  half  normal  size. 
Within  the  egg  capsule  were  the  disintegrating  remains  of  a  bias- 
torn  ere,  probably  the  companion  of  the  one  that  had  developed. 
The  latest  stage  observed  was  one  where  the  ciliary  band  had 
appeared.  It  was  small  but  otherwise  normal.  In  the  egg  capsule 
was  a  disintegrating  blastomere. 

The  occurrence  of  double  embryos  was  observed  in  a  few 
stages,  but  none  later  than  the  blastula.  The  embryos  seemed 
normal  except  in  size. 

These  observations  would  indicate  that  isolated  blastomeres 
in  D.  pusillus  may  develop  into  embryos,  as  they  are  known  to  be 
able  to  do  in  Amphioxus  and  some  other  animals. 

COMPARISON  OF  D.  PUSILLUS  WITH  AMPHIOXUS  WITH  REFERENCE  TO 
ORIGIN  OF  BODY  CAVITIES. 

Since  Bateson  called  attention  to  certain  points  of  similarity 
between  Balanoglossus  and  Amphioxus  various  attempts  have 
been  made  to  further  homologize  the  two  animals.  In  these  dis- 
cussions one  point  has  been  made  much  of,  especially  by  MacBride 
'98,  viz.,  the  similar  origin  of  the  body  cavities.  He  says:  "The 
mesoderm  originates  in  Amphioxus  as  a  series  of  true  gut 


214         University  of  California  Publications  in  Zoology.    [y°L-  4 

pouches,  viz.,  one  anterior  unpaired  pouch  and  two  pairs  of 
lateral  pouches.  Of  these,  the  first  divides  to  form  the  two  head 
cavities ;  the  anterior  pair  give  rise  to  the  first  pair  of  myotomes, 
and  in  addition  to  two  long  canals  extending  back  ventrally ;  the 
posterior  pair  are  gradually  separated  from  the  gut,  and  pari 
passu  divided  into  a  series  of  myotomes.  The  whole  process  of 
mesoderm  formation  is  therefore  referable  to  the  type  found  in 
Balanoglossus,  the  main  difference  being  that  the  pouch  corre- 
sponding to  the  trunk  coelom  of  Balanoglossus  becomes  seg- 
mented." Pp.  606-607. 

He  reproduces,  though  somewhat  modified,  the  diagram  which 
Bateson  '84  (fig.  40)  used  to  illustrate  the  body  cavities  of  Balan- 
oglossus. When  seen  side  by  side,  Bateson Js  diagram  of  the  body 
cavities  of  Balanoglossus  and  MacBride 's  diagram  of  the  body 
cavities  of  Amphioxus  are  strikingly  similar.  If  one  were  to 
judge  by  these  the  homology  of  the  cavities  of  the  two  animals 
would  seem  to  be  well  established. 

Recently  MacBride 's  work  has  been  questioned.  Cerfontaine, 
'05,  says  of  MacBride  's  contention  that  in  Amphioxus  the  meso- 
blast  occurs  in  five  diverticula :  '  '.Je  dirai  des  a  present,  que, 
dan  mes  nombreuses  preparations  je  n'ai  jamais  vu,  quoi  que  ce 
soit,  qui  puisse  avoir  des  rapports  avec  une  semblable  evolution 
du  mesoblaste  chez  1'Amphioxus,  et  je  dois  encore  une  fois  repeter 
que  certaines  figures,  qui  accompagnent  le  memoire  de  MacBride 
denotent,  tvidemment,  une  mauvaise  conservation  du  material." 
p.  364.  "L'ebauche  du  mesoblaste,  existe  sur  tout  le  pourtour 
1'ebauche  notochorde.  Cette  ebauche  du  mesoblaste,  au  moment 
de  I'achevement  des  phenomenes  de  gastrulation,  presente,  avec 
1'orifice  d'invagination  des  rapports  tels,  qu'on  doit  distinguer 
chez  I'Amphioxus,  mangre  1'absence  des  cellules  polaires  de 
Hatschek,  un  mesoblaste  gastral  et  un  mesoblaste  prostomial. " 
p.  389.  With  such  a  disagreement  as  to  the  origin  of  the  meso- 
derm in  Amphioxus  it  would  be  difficult  to  homologize  the  body 
cavities  of  this  animal  and  those  of  Balanoglossus  even  if  Bate- 
son's  account  of  the  latter  be  accepted.  But  the  difficulty  grows 
into  an  impossibility  if  I  have  made  my  case  as  to  the  origin  of  the 
cavities  of  D.  pusillus  and  as  to  the  improbability  that  they  arise 
differently  in  D.  kowaleveskii  from  what  they  do  in  D.  pusillus. 


1908]  Davis. — Life-history  of  Doliclioglossus.  215 

If  we  are  looking  for  types  having  a  development  of  body 
cavities  similar  to  that  found  in  D.  pusillus  we  must  take  into 
consideration  Annelids  and  Molluscs.  In  both  of  these  groups 
the  general  plan  of  mesodermal  development  as  shown,  for  ex- 
ample, by  Wilson,  for  Annelids  and  by  Conklin  for  Molluscs  may 
be  briefly  stated  as  follows :  The  development  of  body  cavities  is 
from  in  front  backwards.  The  mesodermal  bands  posterior  to 
cavities  already  formed  are  undifferentiated  and  "new  cell  ma- 
terial continues  to  be  formed  here  in  the  vicinity  of  the  primitive 
mesoderm  cells." 

The  development  of  the  body  cavities  in  D.  pusillus,  as  I  have 
shown,  follows  in  a  very  general  way  the  above  plan.  But  I  do 
not  wish  in  making  this  comparison  to  suggest  any  homology. 
On  the  contrary,  I  wish  rather  to  emphasize  the  great  difficulty 
in  the  present  state  of  our  knowledge  of  establishing  any  homo- 
logies  whatever  for  these  structures. 


216         University  of  California  Publications  in  Zoology.    [VOL.  4 


BIBLIOGRAPHY. 

BATESON,  WILLIAM 

'84.     The  early  stages  in  the    development    of    Balanoglossus.     Quart. 

Journ.  Micro.     Sc.  n.s.     Vol.  24,  pp.  207-235. 
'85.     The  later  stages  in  the  development  of  Balanoglossus  Kowalevskii, 

with   a   suggestion   as  to   the   affinities   of   the   Enteropneusta. 

Quart.  Journ.  Micro.  Sc.  Vol.  25,  sup.  pp.  1-42. 

CASTLE,  W.  E. 

'96.  The  early  embryology  of  Ciona  intestinalis  Flemming  (L.).  Bui. 
Mus.  Comp.  Zool.,  Harvard  College,  Vol.  27,  no.  7. 

CERFONTAINE,  PAUL 

'05.  Eecherches  sur  le  developpement  de  1'Amphioxus.  Arch,  de  Bi- 
ologie,  t.  22,  pp.  229-418. 

CONKLIN,  E.  G. 

'97.     Embryology  of  Crepidula.     Jour,  of  Morph.,  Vol.  13. 
'05.     The  organization  and  cell  lineage  of  the  Ascidian  egg.    Jour.  Acad. 
of  Nat.  Sc.  Philadelphia,  2nd.  series,  Vol.  13,  part  1. 

JENNINGS,  HERBERT  S. 

'04.  Contributions  to  the  study  of  the  behavior  of  the  lower  organisms. 
Washington:  Carnegie  Institution,  pp.  1-256  . 

MACBRIDE,   E.  W. 

'98.  The  early  development  of  Amphioxus.  Quart.  Journ.  Micro.  Sc. 
Vol.  40,  pp.  589-612. 

MORGAN,  T.  H. 

'94.  The  development  of  Balanoglossus.  Journ.  of  Morph.  Vol.  9,  pp. 
1-86. 

BITTER,  WM.  E. 

'02.  The  movements  of  Enteropneusta  and  the  mechanism  by  which 
they  are  accomplished.  Biolog.  Bui.,  Vol.  3,  pp.  255-261. 

BITTER,  WM.  E.,  and  DAVIS,  B.  M. 

'04.  Studies  on  the  ecology,  morphology,  and  speciology  of  the  young  of 
some  Enteropneusta  of  Western  North  America.  Univ.  of 
Cal.  Pub.,  Zool.,  Vol.  1,  pp.  171-210. 

SPENGEL,  J.  W. 

'77.     Ueber   den   Bau   und   die   Entwicklung   des   Balanoglossus.     Amtl. 

Ber.  d.  Vers.     D.  Naturf.  Aerzte.  pp.  176-177. 
'93.     Die  Enteropneusten  etc.     Fauna  u.  Flora  des  Golfes  von  Neapel. 

18  Monographic. 

WILSON,  E.  B. 

'91.     The  Origin  of  the  Mesoblast-Bands  in  Annelids.     Journ.  of  Morph. 

Vol.  4,  pp.  205-219. 
'93.     Amphioxus    and    the    mosaic    theory    of    development.     Journ.     of 

Morph.  Vol.  8,  pp.  579-638. 


1908]  Davis. — Life-history  of  Dolichoglossus.  217 


ABBREVIATIONS  USED  IN  THE  FIGURES. 


a.  Archenteric  cavity. 

a.m.  Anlage  of  mesoderm. 

b.c.  1,  2,  and  3 :  first,  second,  and  third  body  cavities  respectively. 

ec.  Ectoderm. 

en.  Endoderm. 

ent.  Enteron. 

g.c.  Gland  cell. 

m.  Mesoderm. 

m.f.  Muscle  fibers. 

n.  Nerve  cord. 


EXPLANATION  OF  PLATES. 


PLATE  4. 

Fig.  1  shows  adult  animal  partly  in  mud,  with  one  end  (anterior  lifted 
and  turned  aside  showing  burrow  and  the  eggs  clinging  to  one  side — the 
unbroken  side  of  the  burrow).  X  1,  sketched  from  life. 


1218] 


UNIV.   CAL.    PUBL.  ZOOL  VOL,  4 


[DAVIS]   PLATE  4 


PLATE  5. 

Fig.  2.  Unsegmented  egg,  actual  size  264^ 

Fig.  3.  First  cleavage,  greatest  diameter  420/i 

Fig.  4.  Second  cleavage,  greatest  diameter  420/j. 

Fig.  5.  Third  cleavage,  greatest  diameter  360^ 

Fig.  6.  Fourth  cleavage,  greatest  diameter  360^ 

Fig.  7.  Fifth  cleavage.     Cleavage  pore  shown,  384^ 

Fig.  8.  Sixth  cleavage.     Cleavage  pore  shown,  384/i 

Fig.  9.  Seventh  cleavage,  360^ 


[2201 


UNIV.   CAL.   PUBL.   ZOOL.   VOL.  4 


[DAVIS]    PLATE  5 


8 


PLATE  6. 

Fig.  10.  Gastrula,  early  stage,     (a)    Looking  toward  blastopore.     (b) 
Side  view,  300/t 

Fig.  11.  Gastrula,  late  stage,  looking  toward  the  blastopore,  300^ 

Fig.  12.  Period  I  soon  after  appearance  of  ciliary  band,  long  axis,  300^, 

Fig.  13.  Period  I  soon  after  appearance  of  groove,  long  axis  336^i 

Fig.  14.  Period  I  at  time  of  hatching,  384M 

Fig.  15.  Period  IT,  latter  part,  long  axis  384/x,   (partly  contracted). 

Fig.  16.  Period  III,  second  phase,  long  axis  540/4   (average). 


|222| 


UNIV.   CAL.   PUBL.  ZOOL   VOL  4 


[DAVIS]    PLATE  6 


15 


16 


PLATE  7. 

Fig.  17.  a.  b.  c.  Diagrams  showing  escape  of  larva  from  egg  capsule. 
X  190. 

Fig.  18.     Section  of  blastula.     X  190. 

Fig.  19.     Section  of  gastrula,  early  stage.     X  190. 

Fig.  20.     Section  of  gastrula  just  before  closure  of  blastopore.     X  190. 

Fig.  21.  Section  of  larva  immediately  succeeding  closure  of  blasto- 
pore. X  190. 

Fig.  22.  Sagittal  section  of  larva  at  the  beginning  of  two-walled  cylin- 
der stage,  showing  rapid  growth  of  cells  in  archenteric  wall.  X  190. 


[224| 


UNIV.    CAL    PUBL,   ZOOL.   VOL.  4 


[DAVIS]    PLATE   7 


PLATE  8. 

Fig.  23.  Horizontal  section  of  somewhat  older  larva  than  that  repre- 
sented in  fig.  22.  Here  further  irregularity  appears  among  cells  at  anterior 
of  archenteric  wall.  X  190. 

Fig.  24.  Horizontal  section  of  larva.  Here  the  irregular  disposition  of 
cells  indicated  in  fig.  23  is  still  shown  but  with  a  tendency  to  grow  back- 
ward between  the  ectoderm  and  endoderm  or  archenteric  wall.  This  wedge 
of  cells  is  the  anlage  of  the  mesoderm.  X  190. 

Fig.  25.  Horizontal  section  of  larva.  Here  the  wedge  of  cells  has 
reached  beyond  the  collar  region.  X  190. 

Fig.  26.  Horizontal  section  of  larva  showing  formation  of  second  body 
cavity.  X  190. 

Fig.  27.  Transverse  section  of  larva  somewhat  older  than  that  figured 
in  26.  Section  cuts  across  second  body  cavity.  X  190. 

Fig.  28.  Horizontal  section  of  larva  showing  formation  of  third  body 
cavity,  and  the  relation  of  the  three  body  cavities  to  one  another.  X  190. 

Fig.  29.  Part  of  similar  section  of  same  larva  figured  in  28  but  more 
enlarged.  This  figure  shows  communication  between  cavities  1  and  2,  and 
3.  X  300. 


[226] 


UNIV.   CAL.    PUBL  ZOOL.   VOL  4 


[DAVIS]    PLATE  8 


UNIVERSITY  OF  CALIFORNIA  PUBLICATIONS- (CONTINUED) 

AMERICAN  ARCHAEOLOGY  AND  ETHNOLOGY.— Continued. 

Vol.  7.    No.  1.    The  Emeryville  Shellmound,  by  Max  Uhle.     Pages  106, 

Plates  12,  June,  1907 Price,     1.25 

No.  2.  Recent  Investigations  bearing  on  the  Question  of  the 
Occurrence  of  Neocene  Man  in  the  Auriferous  Gravels  of  the 
Sierra  Nevada,  by  William  J.  Sinclair.  Pages  25  Plates  2, 
February,  1908 Price,  .35 

ASTRONOMY.— W.  W.  Campbell,  Editor.     (Lick  Observatory,  Mt.  Hamilton,  Cal.) 
Publications  o!  the  Lick  Observatory.— Volumes  I-V  completed.   Volumes 

VII  and  IX  in  progress.    Volume  VIII  in  press. 
Vo  .  Vi- 
No.  1.    A  Short  Method  of  Determining  Orbits  from  Three  Observations, 

by  A.  O.  Leuschner. 
No.  2.    Elements  of  Asteroid  1900  GA,  by  A.  O.  Leuschner  and  Adelaide 

M.  Hobe. 
No.  3.    Preliminary  Elements  of  Comet   1900  III,  by  R.  H.  Curtiss  and 

C.  G.  Dall. 
Vol.  9:- 

No.  1.    Organization  and   History  of  the  D.  O.  Mills   Expedition  to  the 

Southern  Hemisphere. 

No.  2.    Introductory  Account  of  the  D.  O.  Mills  Expedition. 
No.  3.    Description  of  the  Instruments  and  Methods  of  the  D.  O.  Mills 

Expedition. 
Lick  Observatory  Bulletins.— Volumes  I-III  completed.     Volume  IV  (in 

progress). 

BOTANY.— W.  A.  Setchell,  Editor.     Price  per  volume  $3.50.    Volumes  I  (pp.  418), 

II  (pp.  354),  completed.    Volume  III  (in  progress). 
Vol.  2:— 

No.  12.    Cytological  Studies  in  Cyanophyceae,  by  Nathaniel  Lyon  Gardner. 

Price,    1.00 

No.  13.    On  a  small  Collection  of  Mosses  from  Alaska,  by  J.  Cardot  and 

T.  Theriot Price,      .10 

No.  14.    Some  unreported  Alaskan  Sphagna,  together  with  a  summary  of  the 
Cryptogamic  Work  of  the    University  of  California   Botanical 
Expedition  to  Alaska  in  1 899,  by  William  Albert  Setchell.    Price,      .05 
No.  15.    On  Nutrient  and  Balanced  Solutions,  by  W.  J.  V.  Osterhout.   Price,      .05 
No.  16.    A  Synopsis  of  the  North  American  Godetias,  by  Willis  Linn  Jepson. 

Price,      .40 

Vol.  3:- 

No.     1.    Compositae  of  Southern  California,  by  Harvey  Monroe  Hall.    Price,    3.00 

CLASSICAL  PHILOLOGY.— Edward  B.  Clapp,  William  A.  Merrill,  Herbert  C. 
Nutting,  Editors.  Price  per  volume  $2.00.  Volume  I  (in 
progress) . 

No.   1.     Hiatus  in  Greek  Melic  Poetry,  by  Edward  B.  Clapp.  Price,  $0.50 
No.  2.    Studies  in  the  Si-clause,  by  Herbert  C.  Nutting.        .        .  .60 
No.  3.    The  Whence  and  Whither  of  the   Modern  Science  of  Lan- 
guage, by  Benj.  Ide  Wheeler .25 

No.  4.    On  the   Influence  of   Lucretius  on  Horace,  by  William  A. 

Merrill .25 

No.  5.    The  Priests  of  Asklepios  (A  New  Method  of  Dating  Athenian 

Archons),  by  William  Scott  Ferguson   ....  .50 

No.  6.     Horace's  Alcaic  Strophe,  by  Leon  Josiah  Richardson      .  .25 

No.  7.    Some  Phases  of  the  Relation  of  Thought  to  Verse  in  Plautus, 

by  Henry  W.  Prescott      .  .  "          .50 

ECONOMICS.-A.  C.  Miller,  Editor. 

Volume  I.  Gold,  Prices,  and  Wages  under  the  Greenback  Standard,  by 
Wesley  Clair  Mitchell.  632  pages,  with  12  charts.  March, 
1908 Price,  $5.00 


UNIVERSITY    OF   CALIFORNIA   PU BLICATION S-tCONT! N U ED) 

EDUCATION.— Edited  by  the  Department  of  Education.     Price  per  volume  $2.50. 
Volume  I  (pp.  424).    Notes  on  the  Development  cf  a  Child,  by  Milicent  W. 

Shinn Price,    2.25 

Vol.  II  (in  progress). — No.  1.    Notes  on  Children's  Drawings,  by  Elmer  E. 

Brown Price,       .50 

Vol.  Ill  (in progress). —No.  1.    Origin  of  American  State  Universities,  by 

Elmer  E.  Brown Price,       .50 

No.  2.    State  Aid  to  Secondary  Schools,  by  David 

Rhys  Jones Price,       .75 

Vol.  IV.    Notes  on  the  Development  of  a  Child.    II— The  Development  of 
.    the  Senses  in  the  First  Three  Years  of  Childhood,  by  Milicent 

Washburn  Shinn  (in  press). 
Vol.  V   (in  progress).— No.   I.     Superstition   and   Education,  by  Fletcher 

Bascom  Dresslar. Price,   2.00 

ENGINEERING.— Edited  under  the  direction  of  the  Engineering  Departments. 
This  series  will  contain  contributions  from  the  Colleges  of 
Mechanics,  Mining,  and  Civil  Engineering.  Volume  I  in  progress. 
No.  1.  Bulletin  of  the  Department  of  Civil  Engineering.  I.— Moment 
Diagrams  and  Typical  Live  Loads,  by  Charles  Derleth,  Jr., 
Pages  1-9,  Plate  1.  January,  1907 Price,  .10 

GEOLOGY.— Bulletin  of  the  Department  of  Geology.  Andrew  C.  Lawson,  Editor. 
Price  per  volume  $3.50.  Volumes  I  (pp.  428),  II  (pp.  450), 
III  (475)  and  IV  (462),  completed.  Volume  V  (in  progress). 
9.  Benitoite,  a  New  California  Gem  Mineral,  by  George  Davis  Louderback, 
with  Chemical  Analysis  by  Walter  C.  Blasdale.  Pp.  149-153, 
July,  1907 Price,  .05 

10.  Notes   on   Quaternary    Felidae   from   California,   by  John    F.  Bovard. 

Pp.  155-170,  pis.  13-14,  September,  1907.      .        .        Price,        .15 

11.  Tertiary   Faunas   of  the  John   Day  Region,  by  John  C.  Merriam  and 

William  J.  Sinclair.     Pp.  171-205,  October,  1907.          Price,        .30 

12.  Quaternary  Myriopods  and  Insects  of  California,  by  Fordyce  Grinnell,  Jr. 

Pp.  207-216,  pis.  15-16,  March,  1908.        .        .        .    Price,        .10 

13.  Notes  on  the  Osteology  of  the  Thalattosaurian  Genus  Nectosaurus, 

by  John  C.  Merriam.    Pp.  217-223,  pis.  17-18,  March,  1908. 
Price,        .10 

PATHOLOGY.— Alonzo  Englebert  Taylor,  Editor.     Price  per  volume,  $2.50. 

Volume  I  (pp.  347)  completed. 
Lectures  on  Fermentation,  by  Alonzo  Englebert  Taylor  (Pathology,  Volume 

l,No.  8) Price,    2.00 

PHILOSOPHY.— Volume  I,  completed.    Price,  $2.00. 

UNIVERSITY  OF  CALIFORNIA  CHRONICLE.— An  official  record  of  University 
life,  issued  quarterly,  edited  by  a  committee  of  the  faculty.  Price, 
$1.00  per  year.  Current  volume  No.  X. 

ADMINISTRATIVE   BULLETINS  OF  THE  UNIVERSITY  OF  CALIFORNIA.- 

Edited  by  the  Recorder  of  the  Faculties.  Includes  the  Register,  the 
President's  Report,  the  Secretary's  Report,  and  other  official 
announcements. 

Address  all  orders,  or  requests  for  information  concerning  the  above  publications 
to  The  University  Press,  Berkeley,  California. 

European  agent  for  the  series  in  American  Archaeology  and  Ethnology,  Classical 
Philology,  Education,  Philosophy,  and  Semitic  Philology,  Otto  Harrassowuz,  Leipzig, 
For  the  series  in  Botany,  Geology,  Pathology,  Physiology,  Zoology  and  also  American 
Archaeology  and  Ethnology,  R.  Friedlaender  &  Sohn,  Berlin. 


NON-CIRCULATING  BOOK 


CD31 


20006, 


UNIV 

5m-9,'26 


jRARY 


